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Cell Biology International (2002) 26, 971–983 (Printed in Great Britain)

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EXPRESSION AND REGULATION OF SPARC, FIBRONECTIN, AND COLLAGEN IV BY DEXAMETHASONE IN LENS EPITHELIAL CELLS

Rajinder S. Sawhney^f1

Department of Pharmacology & Therapeutics, Roswell Park Cancer Institute, Elm & Carlton Streets, Buffalo, NY 14263, U.S.A.

Abstract

Cataract formation is a deleterious side effect of some hormone therapies, thus, it is important to understand how hormones regulate lens basement structure and function. We have examined the effects of dexamethasone (DEX) on the regulation of Secreted Protein Acidic and Rich in Cysteines (SPARC), fibronectin (FN), and collagen IV (CN IV). To radiolabel newly synthesized proteins, cultured monolayers of bovine anterior lens capsule epithelial (ALCE) cells were pulsed with [3H] proline. To identify proteins, an immunofluorescent technique, immunoprecipitation with specific antibodies, and electrophoretic separation on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were used. DEX increased production of total proteins, whereas it specifically decreased synthesis of FN and CN IV. A decrease in FN and CN IV synthesis by DEX in ALCE cells may decrease adhesion of lens epithelium to the basement membrane (BM), which may in turn cause pathogenesis. Messenger RNAs were identified by Northern blot analyses using specific DNA probes. Treatment of lens epithelial cells with DEX causes a 100–150% up-regulation of SPARC mRNA in a concentration-dependent fashion. The increase in the expression of FN mRNA by DEX was in a dose-response fashion and varied from 50–600%. A 24-hour treatment with DEX (10−6M) increased CN IV mRNA levels to 386% over baseline levels. Thus showing a differential upregulation by DEX of mRNAs of SPARC, FN, and CN IV. Results of nuclear run-on transcription assays indicate that regulation of RNAs by DEX may occur, in part, at the transcriptional level. The aberrant expression of lens basement membrane proteins by DEX may contribute to abnormal lens cell function and ultimately to anterior subcapsular cataract.

Key words: basement membrane, cataractogenesis, epithelial cells, lens capsule, gene regulation..

^f1To whom correspondence should be addressed: Tel.: +1 (716) 8455874; Fax: +1 (716) 845-8857; E-mail:rajinder.sawhney@roswellpark.org

Received 5 December 2001; accepted 23 July 2002